A helmet of a glass fiber reinforced thermosetting plastic (hereinafter referred to as GFRP) is widely used as a safety helmet, particularly, that for motorcycles. Recently, a helmet for motorcycles which has become sophisticated as a motorcyclist's outfit has become fashionable, and it tends to become large-sized gradually from the viewpoint of improvement of safety. However, since GFRP is relatively heavy, there is a limit to produce a large-sized helmet. Then, a helmet of a fiber reinforced plastic (FRP), which is rendered lightweight and large-sized by using aramid fibers having high tenacity and high modulus, general-purpose organic fibers (e.g., vinylon fibers, etc.) and the like in combination with GFRP as reinforcements to reduce the amount of glass fibers used, has been already marketed.
A helmet made of this kind of FRP has shock resistance and penetration resistance comparable to those of the conventional GFRP helmet and it can meet lightweight and large size requirements. However, there is a disadvantage that it costs too much because a large amount of expensive fiber materials is used. That is, in comparison with vinylon fibers, fibers having high tenacity and high modulus such as aramid fibers are very expensive.
Further, among organic fibers, aramid fibers have a relatively larger specific gravity and, as a matter of course, there is a limit to produce a lightweight helmet. Furthermore, since cutting properties of aramid fibers are inferior, there is a disadvantage that trimming or punching workability in the production of a helmet is inferior and, therefore, the amount thereof to be used as the reinforcement is considerably limited. Then, in order to obtain sufficient penetration resistance and shock absorption properties, a large amount of vinylon fibers and the like, which have less reinforcing effect, should be used in combination with aramid fibers. However, since, compared to aramid fibers, the specific gravity of vinylon fibers are also large and, consequently, the component of a helmet becomes thick. Therefore, the lightweight requirement can not be fully satisfied and any satisfactory product has not yet been obtained.